Why do MWP-naysayers believe proxy models that don't pick up post-1990 warming?
http://www.climateaudit.org/?cat=5...
Answer:
That title contains too many large words.
I`m sure you have graphs and models that support your view.
give us a link to YOUR research.
And I`ll show you mine.
For openers, I do believe we are seeing a climate shift, 'kay?
However, I am not certain that there is adequate evidence to confirm that this is shift is the result of human activity, at least the "correctable" human activity.
Forest fires, wars (remember the burning oil fields of Kuwait?), and natural events (vulcanism, the exhalations of oceanic biomass, etc.) may have more to do with the warming trend than the emissions from Joe Average's tailpipe.
This is not to say that we should not be aware and take what steps we can to modulate the climate ... for the practice if nothing else (who knows, we may really need to make corrections).
However, the near-hysteria and the bogeyman news items on this issue are not promoting sound science. Why, one alleged scientist even proposed setting off nukes to create a nuclear-winter effect to offset global warming ... there's a solution for you, huh?
I suspect that the "naysayers" are simply hoping for a more effective, and definitive, approach.
I am confused by your question. Not sure what your asking. Your link is for what? I thought maybe it was evidence to show some change in climate but if it is it only would be to one small area. Unless you poked a hole in every tree on earth you could not begin to make a guess at an average of any thing. You also would have to take into account rain fall, humidity and any other thing that affected tree growth. This would also be weak because it leaves out places that have no trees such as the poles, desert areas, and grass lands.
It is human nature to select the data that supports our preconceptions. It's also a classic debating technique.
Most of us--myself included--lack the training to understand the complexities of the global climate, so we have to rely on the scientific assessments that are at our disposal. Mainstream climatologists seem to agree that global warming is occurring and that one factor is human activity, but there is some dissent.
Those with political axes to grind choose the assessments that support their position. I stay out of those arguments, listen, and try to learn.
All of this is part of the larger question humanity's responsibility to refrain from harming the environments in which we live--to make as few messes as we can and to clean up after ourselves as best as we are able.
With buisiness, both of those invole spending money on which no return can be hoped for, so when it is society's interest to make sure these jobs get done, the government has to either regulate the industries or clean up the messes itself.
The first approach angers the business community with its huge resouces for lobbying and campaign contributions and the second one increases our taxes, which angers the voters. Often the politicians take the cowards' way out and simply do nothing at all.
So it is with climate change. It is far easier to latch onto the dissenter's views and minimalize the problem than to take any real action.
Climate modelling is about making future predictions and this is notoriously difficult, that's why the various reports about what the future holds in store vary so much.
If we take data sets from about 1000 years ago and feed them into a modelling programme it will show the MWP. What couldn't be predicted is the subsequent events that would bring about the end of the MWP and a period of 'global' cooling.
In any event, modelling isn't about proving or disproving the existence or causes of global warming. We've incorrectly predicted future population changes, it doesn't mean we don't exist.
Global warming scientists do believe the MWP, of course. They consider it, just as they consider the sun, etc. It just doesn't resemble the current warming. 10 different peer reviewed studies. The graph cuts off in 2004, if it went to 2006 it would be even more impressive.
http://www.globalwarmingart.com/wiki/ima...
Tree-ring data is just one of many components used in a multi-proxy reconstruction of past temperatures, and it's the most uncertain. Several important caveats must be borne in mind when using tree-ring data for palaeoclimate reconstructions.
Not least is the intrinsic sampling bias. Tree-ring information is available only in terrestrial regions, so is not available over substantial regions of the globe, and the climate signals contained in tree-ring density or width data reflect a complex biological response to climate forcing.
Non-climatic growth trends must be removed from the tree-ring chronology, making it difficult to resolve time-scales longer than the lengths of the constituent chronologies.
Furthermore, the biological response to climate forcing may change over time. There is evidence, for example, that high latitude tree-ring density variations have changed in their response to temperature in recent decades, associated with possible non-climatic factors. By contrast, some scientists (Vaganov 1999, below) have presented evidence that such changes may actually be climatic and result from the effects of increasing winter precipitation on the starting date of the growing season.
Carbon dioxide fertilization may also have an influence, particularly on high-elevation drought-sensitive tree species, although attempts have been made to correct for this effect where appropriate.
Thus climate reconstructions based entirely on tree-ring data are susceptible to several sources of contamination or non-stationarity of response. For these reasons, investigators have increasingly found tree-ring data most useful when supplemented by other types of proxy information in “multi-proxy” estimates of past temperature change.
Briffa, K.R., 2000: Annual climate variability in the Holocene: interpreting the message of ancient trees. Quat. Sci. Rev., 19, 87-105.
Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E.A. Vaganov, 1998: Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391, 678-682.
Crowley, T.J. and T. Lowery, 2000: How warm was the Medieval warm period? Ambio, 29, 51-54.
Jones, P.D., K.R. Briffa, T.P., Barnett and S.F.B. Tett, 1998: High-resolution palaeoclimatic records for the last millennium: interpretation, integration and comparison with General Circulation Model control run temperatures. The Holocene, 8, 455-471.
Mann, M.E., R.S. Bradley and M.K. Hughes, 1998: Global-scale temperature patterns and climate forcing over the past six centuries. Nature, 392, 779-787.
Mann, M.E., R.S. Bradley, and M.K. Hughes, 1999: Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations. Geophys. Res. Lett., 26, 759-762.
Mann, M.E., R.S. Bradley and M.K. Hughes, 2000: Long-term variability in the El Nino Southern Oscillation and associated teleconnections. In: El Nino and the Southern Oscillation: Multiscale Variability and its Impacts on Natural Ecosystems and Society, H.F. Diaz and V. Markgraf (eds.), Cambridge University Press, Cambridge, UK, 357-412.
Mann, M.E., E. Gille, R.S. Bradley, M.K. Hughes, J.T. Overpeck, F.T. Keimig and W. Gross, 2000: Global temperature patterns in past centuries: An interactive presentation. Earth Interactions, 4/4, 1-29.
Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M. Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, S. Lamoureux, A. Lasca, G. MacDonald, J. Moore, M. Retelle, S. Smith, A. Wolfe and G. Zielinski, 1997: Arctic environmental change of the last four centuries. Science, 278, 1251-1256.
Vaganov, E.A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber and P.P. Silkin, 1999: Influence of snowfall and melt timing on tree growth in subarctic Eurasia. Nature, 400, 149-151.
http://www.grida.no/climate/ipcc_tar/wg1...
http://www.grida.no/climate/ipcc_tar/wg1...
Show me a recent proxy model that doesn't pick up the MWP. Bet you can't. Here's a list of some that do:
Briffa, K.R., 2000: Annual climate variability in the Holocene: interpreting the message of ancient trees. Quat. Sci. Rev., 19(1–5), 87–105.
Briffa, K.R., T.J. Osborn, and F.H. Schweingruber, 2004: Large-scale temperature inferences from tree rings: a review. Global Planet. Change, 40(1–2), 11–26.
D’Arrigo, R., R. Wilson, and G. Jacoby, 2006: On the long-term context for late twentieth century warming. J. Geophys. Res., 111(D3).
Esper, J., E.R. Cook, and F.H. Schweingruber, 2002: Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295(5563), 2250–2253.
Hegerl, G.C., T.J. Crowley, W.T. Hyde, and D.J. Frame, 2006: Climate sensitivity constrained by temperature reconstructions over the past seven centuries. Nature, 440, 1029–1032.
Mann, M.E., R.S. Bradley, and M.K. Hughes, 1999: Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophys. Res. Lett., 26(6), 759–762.
Mann, M.E., and P.D. Jones, 2003: Global surface temperatures over the past two millennia. Geophys. Res. Lett., 30(15), 1820.
Proxy climate data is generally given a 30-year filter to avoid confusing a change in the weather with a change in the climate. Thus it is not surprising that we don't have proxy data from less than 15 years ago; the statistical validity cannot be vouched for, and would not be the same as for the rest of the time data series.
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